This invention relates to silicone resins and photosensitive resin compositions containing the same useful as resist materials.
In the fields of a variety of electronic devices including semiconductor devices that require microfabrication, there is a rising demand for higher density and higher degree of integration of devices and finer patterning has become essential to meet this demand. Moreover, in plasma display panels (PDP), barriers of a high aspect ratio, that is, a high ratio of height to width, are in demand in order to have light of high luminance emitted by enlarging the electric discharge space for display.
A method for obtaining higher resolution in patterning is to use light of shorter wavelength in patterning of photoresists. However, the use of shorter wavelength poses a problem of the depth of focus (DOF) becoming reduced with a drop in sensitivity and aspect ratio. Multi-level resist processes have been proposed to solve this problem. According to a process of this kind, a material such as novolac and polyimide that can be readily dry-etched by oxygen plasma is deposited by spin coating on a substrate and planarized, a resist resistant to dry etching by oxygen is applied to the surface of the planarized layer, a pattern is formed, and then the pattern is transferred to the bottom layer by anisotropic etching by oxygen plasma. As this process yields patterns of a high aspect ratio, developmental works are being conducted extensively on resist materials resistant to oxygen plasma etching.
Resist materials utilizing silicone resins are known to be highly resistant to oxygen plasma etching and, for example, compositions consisting of ladder type polysiloxane esters or polysiloxanes substituted with epoxy-containing alkyl groups and a photosensitive compound capable of generating acid upon exposure to light are proposed in JP 7-56354 (1995)A1 and JP 8-193167 (1996)A1. Moreover, resist compositions containing photosensitive silicone resins that are polysiloxanes to which a diazonaphthoquinonesulfonyloxy group and an azido group are linked are proposed in JP 6-27671 (1994)A1 and JP 6-95385 (1994)A1.
As for the barrier (rib) of a plasma display panel (PDP), a process for constructing a rib with the use of a paste formulated from photosensitive resins and inorganic powders to raise the aspect ratio is described in JP 10-62981 (1998)A1. The photosensitive resins in question are acrylic polymers and the like.
Polyorganosilsesquioxanes are occasionally abbreviated to polysiloxanes and they are known to occur in three types, that is, cage, ladder, and random. Their structures and methods of preparation are described in detail in the specifications of WO98/41566, JP 50-139900 (1975)A1, JP 6-329687 (1994)A1, JP 6-248082 (1994)A1 and elsewhere. A method for introducing functional groups to the ends of these polyorganosilsesquioxanes is also described in detail in the aforementioned WO98/41566.
An object of this invention is to provide photosensitive silicone resins which exhibit excellent performance as resist materials for multi-level resist processes and for forming PDP barriers. Another object of this invention is to provide resist materials which exhibit excellent plasma resistance (resistance to O2-RIE) and form patterns of a high aspect ratio.
This invention relates to silicone resins composed of polyorganosilsesquioxanes whose ends are partly or wholly linked to a triorganosilyl group represented by the following general formula (1) 
(wherein R is a divalent organic group and Rxe2x80x2 is a divalent group or a direct bond).
This invention also relates to the aforementioned silicone resins wherein the polyorganosilsesquioxanes have a repeating unit represented by the following general formula (2) 
(wherein R2 is an unsubstituted or substituted phenyl group) and the average number of repeating units is 2-5,000.
Furthermore, this invention relates to the aforementioned silicone resins wherein the polyorganosilsesquioxanes consist of one type or a mixture of two types or more selected from ladder type, cage type, and mixed cage-ladder type and the weight average molecular weight Mw is 800-100,000 as determined by gel permeation chromatography (GPC) and calibrated against polystyrene.
Still more, this invention relates to the aforementioned silicone resins wherein R is xe2x80x94R1COOX1xe2x80x94 or xe2x80x94R1COOX1xe2x80x94Si(CH3)2xe2x80x94Oxe2x80x94 (wherein R1 is the divalent residue of a polycarboxylic acid or derivative thereof and X1 is a divalent group).
Still further, this invention relates to photosensitive resin compositions formulated from the aforementioned silicone resins and a photogenerator of acid.
Finally, this invention relates to a process for preparing the aforementioned silicone resins which comprises treating polyorganosilsesquioxanes with Xxe2x80x94Si(R3)2xe2x80x94Y or Xxe2x80x94Si(R3)2OSi(R3)2xe2x80x94Y [wherein X and Y are groups capable of linking with carboxyl groups or functional groups capable of reacting with terminal OH groups or terminal OM groups is an alkali metal) of the backbone of polyorganosilsesquioxanes and R3 is a monovalent organic group] to give modified polyorganosilsesquioxanes containing X or Y at all or a part of their terminal positions, and treating the terminal groups with txe2x80x94BuOOCxe2x80x94R1xe2x80x94COOH (wherein txe2x80x94Bu is t-butyl group and R1 is the divalent residue of a polycarboxylic acid or derivative thereof). The group R3 here is a monovalent organic group such as alkyl and aryl, preferably methyl, and R3 in a given molecule may be of the same kind or of two or more kinds.
Photosensitive silicone resins of this invention are structurally polyorganosilsesquioxanes to which a triorganosilyl group represented by the aforementioned general formula (1) is linked to all or a part of the ends of the backbone chain. The backbone chain may be represented by the general formula (R2Si2O3)n and n designates the number of repetition and is 2 or more. Preferable polyorganosilsesquioxanes have a repeating unit represented by the aforementioned general formula (2) and the average number of repeating units is 2-5,000, more preferably 5-500. The group R2 is a monovalent organic group and may be a hydrocarbon group such as aryl and alkyl and an alkoxy group, but R2 is preferably an alkyl group with 1-6 carbon atoms or an unsubstituted or substituted phenyl group, more preferably a phenyl group.
In the triorganosilyl group represented by the general formula (1), R is a divalent organic group and, as indicated by the aforementioned general formula (1), R may be said to contain the residue of a carboxylic acid. The group Rxe2x80x2 designates a divalent group or a direct bond and, in the case of a divalent group, it is linked on the other side to the terminal Sixe2x80x94Oxe2x80x94 group of polyorganosilsesquioxanes. The t-butyl group at the end of of the triorganosilyl group comes off to leave a free carboxyl group behind when it contacts the acid generated from a photogenerator of acid thereby enhancing the the alkali solubility of silicone resins and it is this property that is utilized in patterning.
Carboxylic acids which give the divalent group R include monocarboxylic acids such as benzoic acid and acetic acid and polycarboxylic acids and they are preferably polycarboxylic acids. Such polycarboxylic acids include pyromellitic acid, trimellitic acid, phthalic acid, biphenyldicarboxylic acid, biphenyltetracarboxylic acid, biphenylhexacarboxylic acid, benzophenonedicarboxylic acid, benzophenonetetracarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl ether tetracarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl sulfone tetracarboxylic acid, diphenyl sulfide dicarboxylic acid, diphenyl sulfide tetracarboxylic acid, benzanilidedicarboxylic acid, benzanilidetricarboxylic acid, benzanilidetetracarboxylic acid, benzanilidepentacarboxylic acid, cyclohexanedicarboxylic acid, cyclohexenedicarboxylic acid, succinic acid, adipic acid, maleic acid, and fumaric acid.
In the case of polycarboxylic acids, the carboxyl group not linked to t-butyl group may be present as free carboxyl (xe2x80x94COOH) or in the form of ester or salt. In particular, it is preferable that one of the carboxyl groups forms an ester linkage with Si either directly or through a divalent group X as illustrated by txe2x80x94Buxe2x80x94OOCxe2x80x94R1xe2x80x94COOxe2x80x94Xxe2x80x94Si(Me)2xe2x80x94. Here, the group R in the general formula (1) corresponds to R1xe2x80x94COOX and X is a divalent group such as alkylene or arylene or a direct bond.
In case polycarboxylic acids is tricarboxylic or higher acids, at least one of the carboxyl groups remains intact and it may remain so or it may be converted to the neutral form such as ester and salt. Alkali solubility becomes poorer if the carboxyl group in question exists in the neutral form such as ester. The acid from a photogenerator of acid contributes to enhance alkali solubility by dissociating the t-butyl group and generating a carboxylic acid. In the cases in which patterning is effected by utilizing this phenomenon, there should desirably be a large difference in alkali solubility between the exposed and unexposed regions and, for this reason, the free carboxyl groups are converted to esters, preferably to t-butyl esters by treating with t-butyl alcohol or derivative thereof.
The group R may contain not only the residue of a carboxylic acid but also a part of the residue of a terminal modifier which modifies the ends of polyorganosilsesquioxanes as described above. A suitable terminal modifier can be represented by Xxe2x80x94Si(CH3)2xe2x80x94Y in which Y is a functional group capable of linking to the backbone polyorganosilsesquioxanes and X is a functional group capable of linking to a group such as carboxyl. For example, a terminal modifier represented by Xxe2x80x94Si(CH3)2xe2x80x94Oxe2x80x94Si(CH3)2xe2x80x94Y [wherein Y is a functional group such as epoxy capable of reacting with the terminal OH or OM group (M is an alkali metal)] reacts with polyorganosilsesquioxanes at one end through Y to give polyorganosilsesquioxanes containing X at the other end. The X-terminated polyorganosilsesquioxanes then react with the aforementioned polycarboxylic acid or derivative thereof to give a product whose R contains xe2x80x94CH2xe2x80x94CH(OH)xe2x80x94 in case X is an epoxy group. A variety of groups such as ester and amide can be formed by changing X. In the aforementioned terminal modifier, X and Y may naturally be identical with or different from each other, but one of them needs to be reactive with the terminal group (or terminal group being generated during the reaction) of polyorganosilsesquioxanes and the other needs to be reactive with a group such as carboxyl or derivative thereof. As is apparent from the above description, the backbone polyorganosilsesquioxanes and the triorganosilyl group represented by the general formula (1) are linked not necessarily through a siloxane linkage but through an appropriate group.
Photosensitive silicone resins of this invention can be prepared by utilizing a known reaction. In the case of polyorganosilsesquioxanes containing terminal silanol, for example, the terminal modification is effected by treating the polymers with a monohalide such as Xxe2x80x94Si(CH3)2xe2x80x94Cl. One of preferable procedures for terminal modification is to treat polyorganosilsesquioxanes such as silanol-free cage type and/or ladder type octaphenylsesquioxane with a terminal modifier such as the aforementioned Xxe2x80x94Si(R3)2xe2x80x94Oxe2x80x94Si(R3)2xe2x80x94X in the presence of an alkali metal catalyst to give X-terminated polyorganosilsesquioxanes.
A silicon atom in polyorganosilsesquioxanes and the silicon atom in a terminal modifier such as Xxe2x80x94Si(CH3)2xe2x80x94Y tend to undergo exchange reaction and a procedure utilizing this property is also effective for terminal modification. In this case, at least one of X and Y needs to be reactive with a carboxyl group. Moreover, it is possible to effect the aforementioned reaction and the exchange reaction simultaneously by using Y as a group capable of reacting with the end of polyorganosilsesquioxanes.
A preferable procedure for preparing silicone resins of this invention from terminally modified polyorganosilsesquioxanes is, for example, to treat the terminally modified polyorganosilsesquioxanes with an acidic ester prepared by the reaction of t-butyl alcohol with a polycarboxylic acid or derivative thereof such as acid anhydride in the presence of a quaternary ammonium salt as a catalyst.
Silicone resins of this invention have a weight average molecular weight of 800-100,000, preferably 5,000-50,000, as determined by GPC and calibrated against polystyrene. The silicone resins in question are solid at normal temperature and soluble in many organic solvents such as esters and ethers. Furthermore, silicone resins of this invention are preferably polyorganosiloxanes represented by the general formula (C6H5S3/2)n having a triorganosilyl group represented by the general formula (1) at all or 10% or more of their replaceable ends, for example, one triorganosilyl group for n=4-20, preferably one for n=2-8.
Silicone resins of this invention are best suited for use as positive resist materials. In such end uses, it is possible to incorporate generators of acid or a variety of additives in order to enhance sensitivity or improve heat or a plasma resistance.
Additives indispensable to photosensitive resin compositions of this invention are photogenerators of acid. Such photogenerators of acid include, but are not limited to, sulfonium salts such as triphenylsulfonium trifluorosulfonate, triphenylsulfonium trifluoromethaneantimonate, triphenylsulfonium benzenesulfonate, and cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, iodonium compounds such as diphenyliodonium trifluoromethanesulfonate, and N-hydroxysuccinimide trifluoromethanesulfonate. A detailed description of the chemical formulas and actions of these photogenerators of acid is found in the aforementioned JP 8-193167 (1996)A1 and xe2x80x9cNew Development of Practical Polymer Resist Materialsxe2x80x9d, p. 57 (in Japanese) published by CMC. A photogenerator of acid is normally added at a rate of 0.2-25% by weight of total solids.
An organic solvent is used to adjust the viscosity. Preferable solvents include, but are not limited to, Methyl Cellosolve acetate, propylene glycol monoethyl ether acetate, methyl lactate, ethoxyethyl acetate, methyl pyruvate, methyl methoxypropionate, N-methylpyrrolidinone, cyclohexanone, methyl ethyl ketone, dioxane, ethylene glycol monomethyl ether acetate, and diethylene glycol monoethyl ether.
Photosensitive resin compositions of this invention contain the aforementioned photosensitive silicone resins and photogenerators of acid as indispensable components and often contain solvents. In addition, it is permissible to incorporate surfactants, colorants, stabilizers, coating improvers, and inorganic powders as needed.
Photosensitive silicone resins of this invention and their compositions can be used as resist materials and barrier materials of PDP. Although there is no restriction on the mode of their use as resist material, they are best suited for multi-level resist processes.
According to a multi-level resist process, a material such as novolac which can be readily dry-etched by oxygen plasma is applied by spin coating to the surfaceof a substrate, a material of this invention is applied thereto, the layers are exposed to a laser such as excimer to generate acid from a photogenerator of acid and let the acid dissociate silicone resins, patterning is effected by developing with an aqueous alkaline solution, and the bottom layer resist is etched by oxygen plasma to give a pattern of a high aspect ratio.
As for the preparation of barrier materials of PDP, methods such as sandblasting, embedding, and photopaste are known. Since any of the methods uses photosensitive resist materials, materials of this inventin can be used as such. In particular, when applied to the photopaste method or the like in which the resist remains unremoved, materials of this invention can fully produce the effect of excellent plasma resistance.